1. Technical Field of the Invention
This invention relates to the regulated epoxidation of propylene. More particularly, this invention relates to a continuous process for the regulated reaction of propylene with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of an epoxidation catalyst to provide propylene oxide and additional tertiary butyl alcohol.
More particularly, this invention relates to a continuous flow controlled process for the preparation of propylene oxide and tertiary butyl alcohol by the continuous reaction of tertiary butyl hydroperoxide with propylene in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst, wherein the process is conducted in a plural stage reactor system comprising a first isothermal segment comprising a plurality of at least four serially connected internally cooled reactors (preferably 5 to 10 reactors) and a second adiabatic segment (preferably containing 4 to 10 serially interconnected reactors).
An initial feed mixture comprising propylene and a recycle stream is continuously charged to a first internally cooled reactor of the isothermal segment, the recycle stream comprising about 25 to about 75 wt. % of the combined weight of the propylene and the recycle stream (and more preferably comprising 40 to 60 wt. %). A plurality of tertiary butyl hydroperoxide feed streams are charged to each of at least four sequentially interconnected internally cooled reactors of the isothermal segment, said tertiary butyl hydroperoxide feed streams comprising a tertiary butyl alcohol solution of tertiary butyl hydroperoxide and molybdenum catalyst.
Reaction conditions of temperature, pressure, internal cooling and time are maintained in the isothermal segment sufficient to provide for a conversion of about 50 to 80 wt. % of the tertiary butyl hydroperoxide (and preferably about 1/2 to 2/3) to thereby provide an intermediate reaction product containing unreacted propylene and unreacted tertiary butyl hydroperoxide.
The said recycle stream is removed from the intermediate reaction product and recycled as aforesaid, the recycle stream being removed in an amount such that it constitutes from about 25 to about 75 wt. % (more preferably about 40 to 60 wt. %) of the initial feed mixture, and the remainder of the intermediate reaction product is charged to the adiabatic segment where the unreacted propylene and the unreacted tertiary butyl hydroperoxide are further reacted with each other under reaction conditions of temperature, pressure, and time sufficient to convert an additional 15 to 30 wt. % of the tertiary butyl hydroperoxide.
Still more particularly, this invention relates to a continuous flow-controlled process for the preparation of propylene oxide and tertiary butyl alcohol, as aforesaid, wherein the initial feed mixture is continuously flowed through an isothermal segment comprising a plurality of at least four serially connected internally cooled reactors, wherein a plurality of at least four tertiary butyl hydroperoxide feed streams is simultaneously charged to at least four sequentially interconnected internally cooled reactors to thereby provide the intermediate reaction product, wherein the said recycle stream is removed from the intermediate reaction product and recycled as described above, and wherein the remainder of the intermediate reaction product is charged to the adiabatic segment wherein an additional 15 to 30 wt. % of the tertiary butyl hydroperoxide is reacted with propylene to provide a final reaction product.
As an example, the isothermal segment may comprise about 10 serially connected internally cooled reactors and wherein six tertiary butyl hydroperoxide feed streams are charged to the first six of the serially interconnected internally cooled reactors. Also, the first of the tertiary butyl hydroperoxide feed streams preferably comprises about 1/2 to 2/3 of the total charge of tertiary butyl hydroperoxide to the isothermal segment.
The reaction conditions established in each of the isothermal and adiabatic segments may suitably include a temperature of about 100.degree. to about 140.degree. C. and more preferably about 110.degree. to about 130.degree. C. The pressure may suitably be in the range of about 200 to 700 psig and more preferably in the range of about 500 to 700 psig. The reaction time may suitably be from about 0.5 to 4 hours and, more preferably, from about 0.5 to 2 hours.
In practice, a desirable reaction temperature and pressure suitable to provide a desired reaction rate are predetermined and both the capacity and the cooling capacity of the internally cooled reactors are correlated with flow rate (i.e., reaction time) so that the predetermined temperature can be maintained throughout the isothermal and adiabatic segments.
2. Prior Art
The reaction of an olefin such as propylene with a hydroperoxide such as tertiary butyl hydroperoxide in solution in a solvent such as tertiary butyl alcohol in the presence of a soluble molybdenum catalyst is disclosed in Kollar U.S. Pat. No. 3,351,635. Kollar teaches that in general, from about 0.5 to 100 moles of olefin may be used per mole of hydroperoxide, the preferred molar ratio being within the range of about 2 to about 10 moles of olefin per mole of hydroperoxide.
Marquis et al. in U.S. Pat. No. 4,891,437 disclose an improvement on the Kollar process in the reaction of propylene with tertiary butyl hydroperoxide is concerned wherein the reaction is conducted in a medium composed of 60 wt. % or more of polar components which is formed by utilizing a molar ratio of propylene to tertiary butyl hydroperoxide of about 0.5 to 2 moles of charged propylene per mole of charged hydroperoxide, the reaction being conducted in solution in tertiary butyl alcohol in the presence of a molybdenum catalyst. Variations in the Marquis et al. process and in the preparation of catalysts useful therefore are disclosed in Marquis et al. U.S. Pat. No. 4,845,251 and U.S. Pat. No. 5,107,067.
British Patent No. 1,298,253 discloses a process for the staged reaction of propylene with tertiary butyl hydroperoxide in the presence of tertiary butyl alcohol and a soluble molybdenum catalyst wherein the reaction product from the first stage is fractionated to provide a lighter fraction which is recycled to the beginning of the first stage and a heavier fraction which is charged to the second stage of the epoxidation process.
Marquis et al. U.S. Pat. No. 4,992,566 and Marquis et al. U.S. Pat. No. 5,093,506 disclose single stage processes for the reaction of propylene with tertiary butyl hydroperoxide wherein the reaction product is fractionated to provide a propylene stream for recycle.
Russell U.S. Pat. No. 3,418,340 discloses a process for the production of propylene oxide by the reaction of propylene with tertiary butyl hydroperoxide involving a recycle of the propylene wherein the propylene is further fractionated to remove oxygen prior to recycle.
Stein et al. U.S. Pat. No. 3,849,451 discloses a process wherein propylene is reacted with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in a single stage compartmented reactor operated under conditions such that propylene and propylene oxide are vaporized during the course of the reaction and wherein the vapors are recovered and distilled to provide a propylene fraction for recycle.
D'Aubigne et al. U.S. Pat. No. 4,002,687 discloses a process for the hydroperoxidation of a hydrocarbon such as isopentane or isobutane with oxygen using a plurality of stages with water washing between stages.